A Randomized, Double-blind, Placebo-controlled Phase 2a Study to Evaluate a Range of
Dose Levels and Vaccination Intervals of Ad26.COV2.S in Healthy Adults Aged 18 to 55
Years Inclusive and Adults Aged 65 Years and Older and to Evaluate 2 Dose Levels of Ad26.COV2.S in Healthy Adolescents Aged 12 to 17 Years Inclusive

Adults:
1. Participant is 18 to 55 years of age, inclusive, or 65 years of age or
older on the day of signing the ICF.
2. Participant must have a body mass index (BMI) <30.0 kg/m2.
3. Participant 18 to 55 years of age, inclusive: Participant must be
healthy, in the investigator's clinical judgment, as confirmed by medical
history, physical examination, and vital signs performed at screening,
and must not have comorbidities related to an increased risk of severe
COVID-19, except for smoking, which is allowed.
Participant 65 years of age and older: in the investigator's clinical
judgment, participant must be either in good or stable health.
Participant may have underlying illnesses, as long as the symptoms and
signs are medically controlled and not considered to be comorbidities
related to an increased risk of severe COVID-19, except for smoking,
which is allowed. If on medication for a condition, the medication dose
must have been stable for at least 12 weeks preceding vaccination and
expected to remain stable for the duration of the study. Participant will
be included on the basis of physical examination, medical history, and
vital signs.
4. All participants of childbearing potential must:
a. Have a negative highly sensitive urine pregnancy test at screening.
b. Have a negative highly sensitive urine pregnancy test immediately
prior to each study vaccine administration.
5. Participant agrees to not donate bone marrow, blood, and blood
products from the first study vaccine administration until 3 months after
receiving the last dose of study vaccine.

Adolescents:
1.Participant is 12 to 17 years of age, inclusive, on the day of signing the ICF
2.Participant must be healthy, in the investigator's clinical judgment, as
confirmed by medical history, physical examination, and vital signs performed
at screening, and must not have comorbidities related to an increased risk of
severe COVID-19
3.Contraceptive (birth control) use by women
4.Participant agrees to not donate bone marrow, blood, and blood products from
the first study vaccine administration until 3 months after receiving the last
dose of study vaccine.

Adults:
1. Participant has a clinically significant acute illness (this does not
include minor illnesses such as diarrhea or mild upper respiratory tract
infection) or temperature >=38.0ºC (100.4°F) within 24 hours prior to the
planned first dose of study vaccine; randomization at a later date is permitted
at the discretion of the investigator and after consultation with the sponsor.
2. Participant has a history of malignancy within 5 years before screening
(exceptions are squamous and basal cell carcinomas of the skin and carcinoma in
situ of the cervix, or malignancy, which is considered cured with minimal risk
of recurrence).
3. Participant has a known or suspected allergy or history of anaphylaxis or
other serious adverse reactions to vaccines or their excipients (including
specifically the excipients of the study vaccine).
4. Participant has abnormal function of the immune system.
5. Participant has a history of any neurological disorders or seizures
including Guillain-Barré syndrome, with the exception of febrile seizures
during childhood.
6. Participant has a history of chronic urticaria (recurrent hives), eczema or
adult atopic dermatitis.
7. Participant received treatment with immunoglobulins in the 3 months or blood
products in the 4 months before the planned administration of the first dose of
study vaccine or has any plans to receive such treatment during the study.
8. Participant is a woman who is pregnant, breastfeeding, or planning to become
pregnant within 3 months after the last dose of study vaccine.
9. Participant has chronic active hepatitis B or hepatitis C infection per
medical history.
10. Participant previously received a coronavirus vaccine.
11. Participant has a positive diagnostic test result for past (serological
testing) or current (PCR based viral RNA detection) SARS-CoV-2 infection at
screening.
12. Participants with comorbidities that are or might be associated with
an increased risk of progression to severe COVID-19, ie, participants with
moderate-to severe asthma; chronic lung diseases such as chronic obstructive
pulmonary disease (COPD) (including emphysema and chronic bronchitis),
idiopathic pulmonary fibrosis and cystic fibrosis;
diabetes (including type 1, type 2, or gestational); serious heart conditions,
including heart failure, coronary artery disease, congenital heart disease,
cardiomyopathies, and pulmonary hypertension or high blood pressure; obesity
(BMI >= 30 kg/m2); chronic liver disease,including cirrhosis; sickle cell
disease; thalassemia; cerebrovascular disease; neurologic conditions
(dementia); and participants who live in nursing homes or long-term care
facilities. This list is consistent with the
list of conditions that increase the risk of progression to severe COVID19
available at the CDC website at the time of writing of this protocol, except
for smoking, which is allowed.
Applicable only to participants 65 years of age and older: Participants may
have hypertension of mild severity as long as it is stable and medically
controlled as defined by no change in medication over the past 6 months (except
for issues of tolerability or use of similar drug with same mechanism of
action, eg, thiazides, Beta blockers, Alpha blockers at the same effective
dose).
13. Participant who is currently working in an occupation with a high risk of
exposure to SARS-CoV-2 infection (eg, health care worker or emergency response
personnel who work in close contact with SARSCoV-2 infected patients) or
considered at the investigator's discretion to
be at increased risk to acquire COVID-19 for any other reason.
14. Participant who has had a known exposure to an individual with confirmed
COVID-19 or SARS-CoV-2 infection within the past 2 weeks.
15. History of confirmed SARS or MERS.

Adolescents:
1.Participant has a clinically significant acute illness (this does not include
minor illnesses such as diarrhea or mild upper respiratory tract infection) or
temperature >=38.0ºC (100.4°F) within 24 hours prior to the planned first dose
of study vaccine
2.Participant has a history of malignancy within 5 years before screening
3. Participants who required chronic administration (defined as more than 14
days) of immunosuppressants or other immune-modifying drugs within 6 months
prior to the study vaccination
4.Any serious, chronic, or progressive disease
5.Participant has obesity
6.Participant received treatment with immunoglobulins in the 3 months or blood
products in the 4 months before the planned administration of the first dose of
study vaccine or has any plans to receive such treatment during the study
7.Participant has chronic active hepatitis B or hepatitis C infection per
medical history
8.Exposure to a person with confirmed COVID-19 or SARS-CoV-2 infection within
the past 2 weeks
9.History of confirmed SARS or MERS